Pressure sensors that use a semiconductor piezoresistance effect are small and light, and have high sensitivity, and thus are used broadly in fields such as industrial instrumentation and medicine. In this type of pressure sensor, a diaphragm is formed on a semiconductor substrate. Strain gauges are formed on the diaphragm. The strain gauges are deformed by pressure applied to the diaphragm. The pressure is measured by detecting the changes in resistances in the strain gauges due to the piezoresistance effect.
A pressure sensor wherein a gauge for static pressure detection is positioned optimally in order to reduce crosstalk has been disclosed (Japanese Unexamined Patent Application Publication 2002-277337 (“JP '337”)). The pressure sensor of JP '337 is provided with a static pressure detecting gauge towards the outside of a bonding portion between a sensor chip and a pedestal. Specifically, a square differential pressure diaphragm is formed in the center of the sensor chip. Then a differential pressure sensing gauge is provided at an edge portion or the center portion of the differential pressure diaphragm. A static pressure detecting gauge is provided at the outside of the differential pressure diaphragm.
The provision of a static pressure detecting diaphragm on a semiconductor substrate has also been disclosed (Japanese Unexamined Patent Application Publication H6-213746 (“JP '746”)). In the pressure sensor in JP '746, an annular static pressure diaphragm is formed on the outer periphery of a circular differential pressure diaphragm. Four static pressure strain gauges are formed on the static pressure diaphragm. The four static pressure strain gauges are disposed with equal spacing in the peripheral direction. That is, two static pressure gauges are disposed across from each other with the diffrential pressure diaphragm interposed therebetween. The static pressure sensitivity can be improved through the formation of a static pressure diaphragm.
As described above, piezoresistive elements wherein the resistance is changed through deformation are used as gauges. That is, the resistance of the piezoresistive element changes in accordance with the deformation of the semiconductor substrate that is produced through the pressure. The pressure can be measured by detecting the magnitude of the variations in the resistances using a bridge circuit.
However, the piezoresistive element is used as the gauge is affected by the ambient temperature in the measurement. For example, a thermal stress will be produced through a difference in the coefficient of thermal expansion between the semiconductor substrate and a glass pedestal, or the like. A strain will be produced in the gauge on the semiconductor substrate due to this thermal stress. As a result, a difference in the ambient measurement temperature may cause measurement error.
Additionally, in pressure sensors it is necessary to make the diaphragm small in order to achieve miniaturization. However, the measurement sensitivity is reduced when the diaphragm is reduced in size. For example, the peak value of the stress is constant when the aspect ratio of the static pressure detecting diaphragm (the ratio of the length and thickness) is constant. However, even if the aspect ratio is held constant, the peak amplitude of the stress is reduced when the diaphragm is made smaller. Because of this, it is difficult to obtain adequate sensitivity. In other words, it is difficult to achieve miniaturization of the pressure sensor when the diaphragm is made larger in order to increase the measurement sensitivity.
In this way, there is a problem in that it is difficult to achieve a small high performance pressure sensor.
The present invention was created in order to solve this type of problem area, and the object thereof is to provide a small high-performance pressure sensor.